The conventional process for producing a film coated with a metal oxide thin film, using an apparatus which enables semi-continuous roll-to-roll metal oxide deposition on a ribbon-shaped film by reactive sputtering is characterized by being able to easily obtain a film having a metal oxide thin film of large area and accordingly is industrially very effective. In the process, however, the surface condition of the target changes with time even when the cathode current, the anode current, the temperature of the film feed, the rate of oxygen feed and the rate of argon feed are kept constant. As a result, there occurs a fluctuation of deposition rate and oxidation degree of metal to be adhere to a film, i.e., fluctuation of the light transmittance, adhesion (adhesion between a substrate film and a metal oxide thin film) and sheet resistance of the film produced. Hence, it becomes necessary to always control the cathode current, the anode current or the rate of oxygen feed in order to make the light transmittance, adhesion and sheet resistance of the film constant. However, it has been difficult to always keep, during thin film formation, the rate of oxygen feed or the cathode current and the anode current at their respective optimum levels in order to make constant, in a highly precise manner, the deposition rate and the oxidation degree of a metal oxide to be adhered to a film and thereby to obtain a continuous ribbon-shaped film having uniform light transmittance, uniform sheet resistance and uniform adhesion.